Vacuum tube oscillator



July 17, 1934. B, vmc T 1,966,696

VACUUM TUBE OSC ILLATOR Filed Aug. 5, 1931 WW1 mum, Q COMM }//5 HTToP/WS Ki.

"sustained oscillations. oscillator such as for example, to drive a telephone, it is essential that the amplitude of oscil- Patented July 17, 1934 UNITED STATES FF 1 C E VACUUM TUBE OSCILLATOR Harvard B. Vincent, Ann Arbor, Mich.

Application August 5, 1931, Serial No. 555,229

4 Claims.

My invention relates to controlling circuits for vacuum tube oscillators used for producing For most uses of an lation be kept as small as practicable in order to prevent the emittance of harmonics of the fundamental note being produced by the device;

and the system must be readily adjustable for controlling the frequency of oscillation.

controlling means giving-a constant amplitude of oscillation independent of the frequency adjustment.

My invention consists principally in providing in an oscillator controlling circuit having a frequency control element, a compensating electrical network to control the amplitude of oscillation independently of the frequency controlling means.

My invention also consists in the parts, combinations and arrangements of parts hereinafter described and claimed.

In the accompanying drawing, which forms a part of this specification and wherein like reference symbols refer to like parts wherever they occur:

Fig. 1 is a wiring diagram of a vacuum tube oscillator having its amplitude of oscillation controlled by an electrical network embodying my invention;

Fig. 2 is a diagrammatic View of an alternate form of network; and

Fig. 3 shows another alternate form of network.

The arrangement illustrated in Fig. 1 shows an oscillator device operatively coupled to an amplifier A in such manner that impulses produced by the oscillator will pass through the amplifier before reaching the output. The oscillator comprises a vacuum tube 1 having the usual anode, cathode and control element or grid. Impulses from the anode of said tube pass into a coupling transformer 2 of the amplifier A and a second coupling transformer 3 is provided on the other side of the amplifier for connecting a load thereto. Interposed beresistancehas been interposedbetween the contween the input and output coupling transformers of the-amplifier is a vacuum tube -4 and a potentiometer gain control means 5 for determining the output -volume. Obviously besides building up the note produced by the oscillator, the amplifier- A also serves to make the action of the oscillator circuit independent of the load attached thereto.

An A battery is connected tothe terminals of both tubes for heating the filaments; and a-B battery is likewise connected to bothtubes to w provide the necessary space potential as is-commen in radio practice.

In order to maintain oscillation, a parallel'circuitis run from the anode of the tube through a condenser 6, and coupled to'this condenser is an anti resonant circuitcomprising a variable condenser 7 connected in parallel with an-inductance coils; and connected across'this-circuit' is a transformer 9 which serves .to reverse the phase of thewave-and feed it onto the grid of the vacuum tube in such phase that oscillations are sustained.

With oscillators heretofore designed, a variable denser 6 and the anti-resonant circuit for the purpose of controlling the amplitude of oscillation, the frequency of oscillation being controlled by the anti-resonant circuit. In such systems, if the variable resistance is set at such a value that oscillations of small amplitude are produced when the frequency is low, and then the capacity of the condenser 7 be altered to produce higher frequency, the amplitude of oscillation increases. Such is the case because the impedance 9 of the anti-resonant circuit is:

where R is the resistance of coil 8 and F is the frequency. This impedance obviously increases with the frequency F, becomes larger compared to the variable resistance and hence has more voltage drop across it producing greater amplitude of oscillation. This is undesirable as pointed 1-00 out above, on account of the production of large harmonics. It is, therefore, necessary to readjust the variable resistance to bring the oscillation down again to small values. This involves resetting the resistance with some care each time the frequency is shifted since if the variable resistance is made too large, not enough energy is fed back to the circuit to maintain the oscillation.

With my construction, the usual variable resistance is replaced by a compensating electrical network, one form of which is shown in Fig. 1. This network comprises two resistances 10 and 11, which are connected in series between the condenser and the anti-resonant circuit, and connected across the anti-resonant circuit from a point between the two resistances is a condenser 12.

Since higher frequencies pass more easily through the shunt condenser 12 than do low ones, it is obvious to anyone skilled in the art that the network will provide more attenuation at higher frequencies than at low ones. If the proper values of resistance 10 and 11, and the proper value of capacitance 12 be chosen, the amplitude of oscillation will remain essentially constant as the variable condenser '7 is changed; and hence no manual adjustment is required for the whole oscillation range of frequencies. In one oscillator construction of applicant, which gave very satisfactory results, the element 6 had the value of 2 microfarads, the element 10 had the value of 12,000 ohms, the element 11 had the value of 12,000 ohms and the element 12 had the value of 0.02 microfarads. The size of the elements used depends upon the impedance of the antiresonant circuit 7, 8 and the variation of this impedance with frequency.

The alternate form of network illustrated in Fig. 2 has inductance coils 13 and 14 substituted for the resistances 10 and 11 of the preferred form of network illustrated in Fig. 1; and the network shown in Fig. 3 has a resistance 15 substituted in place of the shunt condenser illustrated in Fig. 2; and it is obvious to anyone skilled in the art that these networks can be made to accomplish the same result as does the preferred form.

Obviously, the arrangements illustrated and described admit of considerable other variations without departing from the spirit of my invention, and accordingly, I do not wish to limit my invention to precise arrangements shown and described.

What I claim is:

1. An oscillation generator comprising a thermionic tube having input and output circuits, frequency control means coupled to one of said circuits and amplitude control means coupling said input circuit to said output circuit, said amplitude control means comprising a plurality of electrical impedance devices in series and a third electrical impedance device shunted across the frequency control means from a point between said first mentioned devices, all of said devices having a fixed electrical magnitude.

2. An oscillation generator comprising a thermionic tube having input and output circuits, a frequency control network coupled to said input circuit, said network including a variable condenser and an inductance coil connected in parallel, a feed back circuit connected between said frequency control network and said output circuit, a plurality of resistances connected in said feed back circuit, and a condenser shunted across the frequency control network from a point in the feed back circuit between the resistances.

3. An oscillation generator comprising a thermionic tube having input and output circuits, a frequency control network coupled to said input circuit, said frequency control network including a variable condenser and an inductance coil con nected in parallel, a feed back circuit connected between said frequency control network and said output circuit, a plurality of inductance coils in said feed back circuit, and a condenser shunted across the frequency control network from a point between the inductance coils.

4.. An oscillation generator comprising a thermionic tube having input and output circuits, an anti-resonant circuit coupled to said input circui'i', said anti-resonant circuit including a variable condenser and an inductance coil connected in parallel, a feed back circuit connected between said anti-resonant circuit and said output circuit, a plurality of inductance coils in said feed back circuit and a resistance shunted across the antiresonantcircuit from a point between the inductance coils.

HARVARD B. VINCENT. 

